In an electrophotographic copying machine, an original to be copied is placed over a transparent platform or support and is exposed to light rays from an exposing system usually provided under the support. The light rays reflected by the original have an intensity in accordance with the contrast of the original and are transmitted and projected onto a surface of a photoreceptor usually formed, for example, on a drum or an endless belt for creating an electrostatic latent image of the original thereon. The photoreceptor is, then, pressed against or rolled over the copy paper in a transferring station for transferring the latent image onto the copy paper. Such copy paper is supplied from a roll of paper which is cut and separated from the roll for every cycle of copying operation, or the copy paper is supplied from a stock of sheets of copy paper. The copy paper now having the latent image transferred thereon in the above described manner is conveyed to a developing station where the latent image is developed with developer material such as toner into a visible toner image. Thereafter, the developed copy paper is conveyed to a fixing station where the visible toner image is fixed by any suitable means such as a heater. Finally, the copy paper is conveyed out of the copying machine through a discharging opening onto a tray provided outside the copying machine.
During the time the copy paper is being conveyed through the various stations, there has been a disadvantage, although the posibility may be low, that the copy paper may be caught at some places in the stations so that the copy paper may become jammed in the copying machine.
One conventional type of detecting device for detecting such jams employs a rotary cam arrangement which simultaneously rotates in accordance with the travel of the copy paper, and detects paper jam through detection of the leading edge of the traveling copy paper by a suitable detecting mechanism. Although, such type of detecting device may function to detect the paper jam, it is necessary to furnish the copying machine with said rotary cam arrangement and detecting mechanism. Thus, the copying machine may become large in size and further complicated in its construction. Furthermore, it is impossible for such type of detecting device to detect a paper jam occuring at the detecting mechanism after the leading edge has been detected, since the detecting mechanism only detects the leading edge of the copy paper.
Another conventional type of detecting device employs timer means and means for detecting the leading edge of the copy paper provided adjacent to a copy paper discharging opening. The timer means measures the time during which the copy paper travels through the copying machine and compares such measured time with a predetermined time for the copy paper to travel through the copying machine. In the case where the measured time exceeds the predetermined time, the timer means produces an alarm signal for actuating an alarm system. In this type of detecting device, it is not necessary to furnish the copying machine with various detecting mechanisms such as a rotary cam arrangement. However, it is necessary to preadjust the timer means according to the length of the copy paper, which arrangement thus results in complication of the timer means. Therefore, this type of detecting device is not suitable for a copying machine designed to employ copy paper of various sizes.